Friday, August 01, 2014
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    Transmission Line (Bailey)

This type of loudspeaker enclosure was proposed in October 1965 by Dr A.R. Bailey and A.H. Radford in Wireless World magazine. The article postulated that energy from the rear of a driver unit could be essentially absorbed, without damping the cone's motion or superimposing internal reflections and resonance, so Bailey and Radford reasoned that the rear wave could be channelled down a long pipe. If the acoustic energy was absorbed, it would not be available to excite resonances. A pipe of sufficient length could be tapered, and stuffed so that the enegy loss was almost complete, minimizing output from the open end. No broad consensus on the ideal taper (expanding, uniform cross-section, or contacting) has been established.

Unlike vented speaker systems, transmission lines are designed to absorb most of the energy radiated from the driver's rear, and if appropriately damped, the line does not form a tuned system. Closed type transmission lines typically have negligible acoustic output from the enclosure except from the driver. Open ended lines exploit the low-pass filter effect of the line, and the resultant low bass energy emerges to reinforce the output from the driver at low frequencies. Well designed transmission line enclosures have smooth impedance curves, possibly from a lack of frequency-specific resonances, but a low efficiency.

Have also a look at my second Transmission Line Calculator

  Qts [ ] possible > 0.45
  Mr [cm] Membrane radius [cm]
  Fs [Hz] Driver resonance frequency Hz
  Ew [cm] Enclosure width inside [cm]


Th [cm] : Tm [cm] : L [cm] :
Ah [cm²] : Am [cm²] :

Th [cm] Depth of the neck opening
Tm [cm] Depth of the mouth opening
L [cm] Line Length
Ah [cm²] Surface of the neck opening
Am [cm²] Surface of the mouth opening

Take a look at 'Definition Transmission Line'